open System
open System.Drawing
open System.Threading

type ScrollLetter = Letter of char | ColouredLetter of char * System.ConsoleColor

let padStr (msg:string) = 
  let screenWidth = Console.WindowWidth in 
  match msg.Length > screenWidth with
  | true -> msg.Substring(0, screenWidth)
  | otherwise -> msg ^ String.make (screenWidth - msg.Length) ' '
  
let leftShiftMsg (msg:ScrollLetter list) = List.append msg.Tail [msg.Head]

let colourSelector c = match c with
  | 'C' -> ConsoleColor.Magenta
  | 'M' -> ConsoleColor.Red
  | 'A' -> ConsoleColor.Yellow
  | otherwise -> ConsoleColor.Green
  
let createMsg (str:string) = 
  let charList = (padStr str).ToCharArray() |> Array.to_list in
  List.map (fun c -> match char.IsUpper c || char.IsPunctuation c with
    | true -> ColouredLetter (c, colourSelector c)
    | otherwise -> Letter c) charList

let printMsg msg = List.iter (fun letter -> match letter with
    | Letter c -> Console.Write c
    | ColouredLetter (c,colour) -> 
      let oldColour = ConsoleColor.White in
        Console.ForegroundColor <- colour;
        Console.Write (String.of_char c);
        Console.ForegroundColor <- oldColour
    ) msg

let rec scroll msg = 
  let newMsg = msg |> leftShiftMsg in
    Console.SetCursorPosition(0, 1);
    printMsg newMsg;
    Thread.Sleep(100);
    scroll newMsg

let _ = createMsg "Congratulations Mark and Amber!!!" |> scroll